function [ ] = mx_eyelink_read_request( )
%MX_EYELINK_READ_REQUEST Sends a text variable name whose value is to be read 
% and returned by the tracker as a text string.
%
% Remarks:
% NEW (v2.1): If the link is initialized but not connected to a tracker, the 
% message will be sent to the tracker set by set_eyelink_address(). However, 
% these requests will be ignored by tracker versions older than EyeLink I v2.1
% and EyeLink II v1.1.
% Parameters:
% text 	String with message to send.
% Returns:
% 0 if success, otherwise link error code.
%
%----------------------------------------------------------------------------
% Copyright Eduardo Aponte 2013
% aponteeduardo@gmail.com